Curing with light was known and used in medicine in ancient times. Red or ultraviolet light was successfully used in the 19th century for the treatment of pockmarks and lupus vulgaris by Danish physician, N. R. Finsen, the father of contemporary phototherapy.
Biological phenomena induced by ultraviolet light have been intensively investigated in photobiology and photomedicine for several decades. Ultraviolet light as a phototherapy for some dermatological diseases (mainly psoriasis) has been used since the early twenties. However, ultraviolet light is an ionizing radiation, and therefore has a damaging potential for biomolecules and has to be used in photomedicine with certain precautions.
Biological and healing phenomena induced by optical wavelength (visible) and infrared (invisible) light have been intensively investigated in the last decade. Electromagnetic waves with optical (visible light) and near infrared (invisible irradiation) wavelengths (.lambda.=400-2,000 nm) provide non-ionizing radiation and have been used in vivo, in vitro and in clinical studies, as such radiation does not induce mutagenic or carcinogenic effects.
Lasers, specific light sources which provide narrow-band monochromatic, coherent, polarized light with wide range of powers and intensities, have been widely used in medicine. Medical lasers may be subdivided into three groups according to their power and ability to produce heat: hot lasers, which are used in surgery; mid power lasers which are used in photodynamic therapy for cancer treatment or in dermatology to treat telangiectasia, port-wine stains, etc.; and low energy (or low intensity, cold or low level) lasers which deliver several orders of magnitude less energy to the tissue than surgical lasers. They produce very little heat in biological tissue or no heat at all.
Low energy lasers have been used in dermatology, traumatology and some other areas to enhance healing phenomena in the body (Mester et al., Lasers Surg. Med. 5:31-39, 1985; Trelles et al., Lasers Surg. Med. 7:36-45, 1987; Ohshiro T., Laser Therapy: Practical Applications, (Ed. T. Ohshiro), John Wiley, Chichester, 1991). The most frequently used terms for this area of physiotherapy are low Energy Laser Therapy (LELT), Low reactive Level Laser Therapy (LLLT), or Laser Therapy. The first successes of LELT were demonstrated in the treatment of chronic ulcers and persistent wounds of different etiology (Mester et al., Lasers Surg. Med. 5:31-39, 1985).
Anecdotal case studies have suggested that LELT is beneficial for a number of dermatological and musculoskeletal conditions. However, LELT has failed to provide good results in well-controlled randomized double-blind studies designed in accordance with rigorous North-American standards (Gogia and Marquez, Ostomy/Wound Management, 38:38-41, 1992; Lundeberg and Malm, Ann. Plast. Surg., 27:53).
Coherence and polarization are the main features which differentiate laser light from regular monochromatic light. Many photoinduced phenomena in cell cultures and biotissue are reported to be induced by noncoherent, nonpolarized monochromatic light (Karu, Health Physics, 56:691-704, 1989 and Karu, IEEE J. of Quantum Electronics, QE23:1703-1717, 1987).
Laser beams lose coherence and polarization because of scattering very quickly after entering tissue and thus deeper tissue layers "do not distinguish" laser from non-laser light.
Low energy photon therapy (LEPT), also known as low energy, low level, low intensity laser therapy, photobiomodulation, is the area of photomedicine where the ability of monochromatic light to alter cellular function and enhance healing non-destructively is a basis for the treatment of dermatological, musculosketal, soft tissue and neurological conditions.
Low energy photons with wavelengths in the range of 400 nm-2,000 nm have energies much less than ultraviolet photons, and therefore, low energy photons do not have damaging potential for biomolecules as ionizing radiation photons have.
The area of LEPT research is controversial and has produced very variable results, especially in clinical studies. Almost every mammalian cell may be photosensitive, e.g. could respond to monochromatic light irradiation by changes in metabolism, reproduction rate or functional activity. Monochromatic light photons are thought to be absorbed by some biological molecules, primary photoacceptors, presumably enzymes, which change their biochemical activity. If enough molecules are affected by photons, this may trigger (accelerate) a complex cascade of chemical reactions to cause changes in cell metabolism. Light photons may just be a trigger for cellular metabolism regulation. This explains why low energies are adequate for these so called "photobiomodulation") phenomena. However, it is difficult to induce and observe these phenomena both in vivo and in vitro using the same optical parameters. Specific optical parameters are required to induce different photobiomodulation phenomena (Karu, Health Physics, 56:691-704, 1989; Karu, IEEE J. of Quantum Electronics, QE23:1703-1717, 1987). The range of optical parameters where "photobiomodulation" phenomena are observed may be quite narrow. The specificity and narrowness of the optical parameters required for "photobiostimulation" in LEPT therapy distinguishes LEPT therapy from the photodestruction phenomena induced by hot and mid power lasers (e.g. in surgery and PDT).
Devices for stimulating biological tissue using low energy light are disclosed for example in U.S. Pat. No. 4,930,504 to Diamantopoulos et al. and U.S. Pat. No. 4,686,986 to Fenyo et al., U.S. Pat. No 4,535,784 to Rohlicek describes an apparatus for stimulating acupuncture points using light radiation. U.S. Pat. No. 4,672,969 to Dew describes a method and apparatus for closing wounds using a laser tuned to a wavelength of 1.33 .mu.m to produce thermal heating of the tissue to denature the protein.
To meet the changing requirements for optical parameters for different experimental and clinical applications, there is a need for an optical system for "photobiomodulation" having flexible parameters, adjustable for particular applications. In particular, there is a need for an apparatus capable of treating a range of biological disorders by reliably providing light to the affected three dimensional biological tissue, which light has the optical parameters necessary for inducing the appropriate photobiomodulation for the particular disorder and tissue to be treated. There is also a need for a method for reliably providing light having such parameters to a biological tissue having a disorder in order to effect healing.